Klebsiella pneumonia carbapenemase (KPC)-producing organisms are an emerging class of multi-drug resistant bacterial pathogens that are either effectively untreatable or only treatable with toxic antimicrobials. Their resistance to carbapenems is especially problematic, as these agents are often the last line of defense against drug-resistant pathogens. Therefore, the CDC now categorizes such carbapenem-resistant Enterobacteriaceae (CRE) in their top antibiotic resistance threat level. New anti-infective strategies are urgently needed. Carbapenemase genes (and resistance to many other antimicrobials) are carried on large, low copy number plasmids. An underlying hypothesis of this proposal is that it should be possible to target these plasmids for eviction, thereby rendering strains carbapenem susceptible. Considered more broadly, this strategy might also be employed to restore resistance to many other antimicrobials as well. Therefore, in one specific aim, proof of principle is sought for combating carbapenemase resistance through plasmid eviction therapy. To accomplish this goal, a screening strategy will be developed, validated, and implemented to identify small molecule inhibitors of plasmid maintenance and restore susceptibility to carbapenems. (1) The screening strategy is based on technology that will allow quantitative assessment of plasmid loss. Specifically, novel transposons will be used to integrate luminescent and fluorescent reporter genes into the carbapenemase resistance plasmid and bacterial chromosome of a screening strain, thereby allowing a normalized measure of plasmid number. (2) A high throughput screen for anti-plasmid agents will then be validated and performed. (3) Potent inhibitors of plasmid maintenance will be tested for their ability to restore carbapenem susceptibility, i.e., adjunctive antimicrobial activity. (4) The principal investigator has a large collection of CRE isolates that will have their genomes sequenced and annotated as part of a collaboration with the Broad Institute CRE genome project. Preliminary sequence analysis suggests potential for shared plasmid maintenance mechanisms that could represent targets for broadly acting anti-plasmid agents. Accordingly, compounds with adjunctive antimicrobial activity will also be tested for activity against this CRE collection to establish the potential for broadly acting therapeutics. Validation of proof of principle would provide rationale and impetus for future large scale screening efforts for lead compound identification and development.